KR100408982B1 - Channel assignment in a spread spectrum cdma communication system - Google Patents

Abstract

The present invention provides a method for sending data in a spread spectrum code division multiple access communication system having a common packet channel using a predetermined set of codes and a base station thereof. The common packet channel has a plurality of access opportunities, each defined by a time slot (30-34) and signature (36-40). The method of the present invention comprises the steps of receiving a signature in the common packet channel, selecting a code out of a plurality of codes associated with the common packet channel, transmitting a combined collision signal and channel identifier, and communicating data using the selected code. According to the present invention, the channel identifier indicates the selected code and the channel identifier is associated with the received signature.

Description

CHANNEL ASSIGNMENT IN A SPREAD SPECTRUM CDMA COMMUNICATION SYSTEM}

1 illustrates a wireless spread spectrum code division multiple access (CDMA) communication system 18. Base station 20 communicates with user equipment (UE) 22-26 in its operating area. In a spread spectrum CDMA system 18, a data signal is carried between the UEs 22-26 and the base station 20 on the same spread bandwidth. At the shared bandwidth, each data signal is spread in unique chipcode order. Upon reception, a specific data signal is recovered using a replica of the chipcode order.

Since signals are identified by chipcode order (code), separate dedicated communication channels are created using different codes. In the downlink channel, signals are transmitted from the base station 20 to the UE 22-26, and in the uplink channel, signals are transmitted from the UE 22-26 to the base station 20. For coherent detection of downlink transmissions by the UEs 22-26, pilot signals are transmitted to all UEs 22-26 within the operating range of the base station. UEs 22-26 adjust their receivers based on pilot signals that enable data reception.

In most CDMA systems, a common packet channel (CPCH) is used for uplink transmission. The CPCH may carry data packets from different UEs 22-26. Each data packet is identified by its code. For detection by the base station 20, the packet has a preamble that can be distinguished from other packets. CPCH is commonly used to deliver data communicated at high speed occasionally.

2 illustrates a CPCH access method 28. The CPCH access method 28 is time-divided into intervals with time slots 34-34, such as eight time slots proposed for the third generation mobile telecommunications system (IMT-2000). A certain group of signatures 36-40 are assigned to time slots 30-34 to allow one or more UEs 22-26 to use the same time slots 30-34. The particular signature used within a particular time slot is called an access opportunity 66-82. For example, in the proposal of IMT-2000, one of sixteen signatures is available for selection of eight time slots each, resulting in 128 access opportunities. Each signature 36-40 is pre-assigned to a virtual channel. The virtual channel defines operating parameters for both uplink and downlink, i.e., uplink spreading factor and unique code of the downlink.

Broadcast from base station 20 to each UE 22-26 is available in each virtual channel via an acknowledgment channel (AICH). The UEs 22-26 monitor the AICH to determine the availability of each virtual channel. Based on the operating parameters required by the UE 22-26 and the availability of the virtual channel, the UE determines the access opportunity to select. When identifying a particular access opportunity, base station 20 issues an acknowledgment message (ACK) if the corresponding downlink channel is still available. In the IMT-2000 proposal, the ACK is a simple repetition of the signature 36-40 associated with the access attempt. If the downlink channel is not available, a negative acknowledgment (NAK) is sent.

After receiving the corresponding acknowledgment, the UE 22-26 determines an appropriate code to recover communication in the downlink channel based on the access opportunity 66-82 used to transmit the packet of the UE. Transmitted in the broadcast channel of the base station or stored in the UE 22-26 is a list of codes assigned to each access opportunity 66-82. This method significantly increases the probability of undesirable packet collisions and thus packet delays.

In some situations, monitoring the AICH is undesirable. At certain moments some UEs 22-26 will operate in a "sleep" mode. In the " sleep " mode the UEs 22-26 only execute when there is a need to transmit data. Monitoring the AICH during "sleep" mode shortens battery life and introduces some delay in the transmission of the first packet. In addition, monitoring multiple AICHs further exacerbates these defects when the UEs 22-26 demarcate between the operating areas of two base stations.

Surveillance creates other problems. Supervision makes UE 22-26 more expensive by making the receiving circuit of the UE more complicated.

Surveillance does not optimize the use of CPCH. AICH supervision provides information when the channel is busy. If the channel is busy it will be the maximum packet length. If the packet is not the maximum length, the channel becomes an idle channel while the UE 22-26 is waiting to transmit. On the other hand, if no monitoring is performed in such a system, channel availability information is not available. UEs 22-26 may randomly select busy virtual channels that increase packet delay by causing collisions. Thus, it is desirable to have the UE 22-26 wait for a period shorter than the maximum packet length to provide some other collision reduction mechanism.

One technique to reduce the likelihood of a collision is to load multiple codes, such as 128 different codes. The 128 order in the proposal for IMT-2000 represents about half of the order available in the base station 20. Thus, such a solution is not desirable. In addition, monitoring of the AICH is undesirable because it increases the code by complicating the UE receiver circuitry. Thus, an alternative method for allocating virtual channels is desirable. WO 9849857 discloses a system for transmitting random access packets from a mobile station to a base station. Each packet to be transmitted to be transmitted by the mobile station in a time slot of a repeating frame is appended with a preamble signature. The preamble signature is a short spreading code associated with a unique long spreading code. The packet including the preamble is received by the base station. The preamble facilitates the recovery of data from packets. The TIA / EIA-95-B "mobile station-base station system" discloses a channel allocation method of a code division multiple access system. The channel assignment message is sent to the mobile station. The message indicates information about the channel, such as the channel's spreading code. Thus, an alternative method for allocating virtual channels is desirable.

TECHNICAL FIELD The present invention relates to resource allocation in wireless code division multiple access communication systems, and more particularly, to assigning an uplink channel and a downlink channel in response to an access request of a user equipment.

1 is a diagram illustrating a typical wireless spread spectrum CDMA communication system.

2 is a diagram illustrating a common packet channel access method.

3 is a diagram illustrating an allocation virtual channel of an example.

4 is a probability graph of a demand versus collision for a virtual channel allocation of the prior art.

5 is a schematic diagram of a base station and user equipment.

6 is a diagram illustrating an identifier transmitter circuit.

7 is a diagram illustrating an identifier receiver circuit.

8 is a diagram illustrating an assignment table in Golay order.

FIG. 9 is a circuit for detecting the high-ray order of FIG. 8.

10 is a diagram illustrating an allocation table for a system of physical channels with two time slots.

The selected user equipment sends the signature in the selected one of the time slots of the common packet channel. The base station receives the transmitted signature and selects a currently unused code from a plurality of codes associated with an access opportunity defined by the selected signature and the selected time slot, if available. The base station transmits an acknowledgment signal containing the identifier of the selected code. The selected user equipment receives an acknowledgment signal. The selected user equipment and the base station communicate using the selected code.

Hereinafter, a preferred embodiment will be described with reference to the drawings. Like reference numerals in the drawings denote like elements. 3 illustrates a virtual channel allocation method. Each virtual channel 48-64 is defined by its operating parameters, such as an uplink spreading factor and downlink code. Additionally, instead of assigning virtual channels 48-64, the same principle can be applied to the assigned physical channels defined by the downlink code.

Each physical channel can be multiplexed using two time slots to reduce the number of physical channels used to increase the power level of each channel. Using two time slots will increase the effective data rate of the channel from 8 Kbps to 16 Kbps. The virtual channel 48-64 in this system also defines which multiplexed signal is assigned to the UE 22-26.

Instead of assigning a single virtual channel for each signature 36-40 as in the prior art, a set of virtual channels 42-46 are allocated for each grouping of access opportunities 116-120. Grouping can include all channels in one less group, such as two or three channels. One possible virtual channel grouping can group all virtual channels at the same data rate for the uplink. For groups with the same uplink data rate, the UEs 22-26 select an access opportunity among the groups with the desired uplink data rate of the UE. Another grouping can be formed based on the signature of access opportunity 36-40. Based on the access request selected and the UE's priority, one of the virtual channels 48-64 assigned to the group 116-120 associated with the access attempt is used for the UE if available. Once a virtual channel is assigned, it will not be reassigned until the transaction of a particular UE is completed. In addition, the receiving circuit of base station 20 having an appropriate data rate is assigned to UEs 22-26.

In conventional systems, UEs 22-26 determine which channel is assigned to the downlink based on access opportunity 66-82. The virtual channel assignment sends channel identifiers 84-88 with an ACK indicating whether the channel sets 42-46 assigned to groups 116-120 are selected. When all virtual channels are in the same group, identifiers 84-88 indicate the selected virtual channel. If the channel is available from sets 42-46, a negative acknowledgment is sent. Since more than one virtual channel is potentially assigned to a particular access attempt, the UE collision probability is reduced.

4 is a graph 91 showing the number of required accesses (demands) versus collision probability of the UEs 22-26. As shown, there are fewer collisions (two states / AP or three states / AP) using two or three channels per group than the prior art (AICH monitor) regardless of the demand.

5 is a schematic diagram of a base station 20 and a UE 22 for use in implementing channel assignment. The UE 22 has a controller 144 for determining communication codes of uplink and downlink. UE transmitter 140 transmits communications such as access opportunities and uplink packet signals to the base station. The UE receiver 142 receives communication such as an ACK message, a NAK message, a downlink signal, and the like.

Base station 20 has a controller 134 for determining uplink and downlink communication codes and channel availability. The base station transmitter 136 transmits communications, such as an ACK message, a NAK message, a downlink signal, to the UE 22. Base station receiver 138 receives communications such as access opportunities and uplink packet signals.

The technique for transmitting the identifier is to change the phase of the ACK or append extra bits to the ACK to indicate the selected identifier. In the case of a system using a single group of virtual channels, the extra bits identify the selected virtual channel. 6 and 7 show a circuit for transmitting an identifier by phase shifting the ACK. The circuit can transmit up to four channel identifiers without a NAK identifier or up to three channel identifiers with a NAK identifier. In the transmitter circuit 92 of FIG. 6, the ACK order is generated by the sequence generator 94. The order itself is related to the preamble access opportunity and is unique to the access attempt. Several such sequences can be sent to several users at the same time. The ACK order passes through a mixer 96 that multiplies the signal by either +1 or -1. The mixed signal is then passed through another mixer 98, which is mixed with a co-phase carrier (cos wt) or quadrature carrier (sin wt). As the signal passes through two mixers 96 and 98, the transmitted ACK is one of four phases 0 °, 90 °, 180 ° and 270 °. Each identifier 84-88 is preassigned to one of four phases.

The receiver circuit 14 of FIG. 7 is used to determine the phase of the ACK sent to the transmitter circuit 92 of FIG. The ACK is mixed with the in-phase carrier by the mixer 100 and the quadrature carrier by the mixer 102. Each mixed signal is correlated with a replica of the order of the ACK by the order correlators 104 and 106. In-phase and quadrature correlation signals are negated by the mixers 108 and 110 by multiplying the correlation signal by -1. Two correlated signals and two negative signals are supplied to the identifier circuit 112. The identifier circuit 112 determines which of the four phase shifts of the correlated signal has the highest magnitude. Since downlink transmissions from the base station are synchronized to know their phase, the identifier circuit 112 determines which identifier 84-88 is transmitted based on the phase of the ACK. The virtual channel 48-64 associated with the identifier 84-88 and the group 116-120 and access point of the UE's access request using a list transmitted on the broadcast channel of the base station or stored in either of the UEs 22-26. It is used to determine. The transmission sent by the base station 20 using the downlink channel code selected by using the determined virtual channel 48-64 is recovered at the UE 22-26.

Another technique for transmitting the identifiers 84-88 is to use an ACK and an outgoing resolution signal (CR). After base station 20 detects a collision between UEs 22-26, in most spread spectrum systems, base station 20 transmits a CR directed to the colliding UE. The CRs have a sequence that is associated with a particular UE 22 for detection by the UE 22. By inverting the ACK and the CR, the identifiers 84-88 are sent to the particular UE 22. Inverted ACK indicates NAK. By inverting the CR, one virtual channel is assigned to + CR and the second virtual channel is assigned to -CR. Thus, an identifier indicating NAK or one of two channels is transmitted using ACK and CR. Additionally, one of the multiple channels is assigned to the CR using a CR with multiple states such as three states.

Alternatively, the identifier is sent with a signal using a high-lay order. The high lay order consists of short order such as X and Y. By inverting the shortening order and changing the order, a majority of the longest order can be constructed as shown in the table 122 of FIG. Only half of the possible order is shown to reduce the size of the table 122. By negating each order, another unique Golay order is the result. As shown in FIG. 8, each UE 22-26 is assigned a unique set of Golay order equal to four. For example, user 0 is assigned in four orders, that is, the top two orders and the negation of this order. By assigning each of the Go-Ray sequences, the receiving UE 22-26 determines the downlink transmission code when the virtual channel is received.

9 shows a high-ray order detector. The received signal is correlated with the high ray correlator 123 and interleaved by the inverver 124 to detect the short code. The assignment of short codes for two assignment orders in the long code is shown as signatures 0 and 1. Using mixers 125 and 126, the signature is mixed with the detected short code. Adders 127 and 128 are coupled to the mixer and delay devices 129 and 130. Delay devices 129 and 130 receive the output of adders 127 and 128 and feed the output back to adders 127 and 128 for correlation with the next shortening order. The output of each adder 127, 128 determines the high-lay order of the received signal.

10 illustrates a method for allocating a system using two time slot multiplexing for a physical channel. In table 132, each of the 16 different signatures is assigned one of a downlink code and two time slots. The selected time slot is indicated by the transmitted identifier.

Claims (27)

A method for transmitting data to a wireless spread spectrum code division multiplexed access communication system 18 between user equipments 22, 24, 26 selected by a plurality of user equipments 22, 24, 26 and a base station 20, The spread spectrum code division multiplexed access communication system 18 has a common packet channel 28 defined by a predetermined set of codes 48-64, the common packet channel having a plurality of access opportunities 66-82. Each access opportunity is defined by a time slot 30-34 and a signature 36-40, wherein the selected user equipment has a signature 36-40 in a selected one of the common packet channel time slots 30-34. And the method, In response to receiving the signature 36-40 sent by the base station 20, a code association between the selected signature 36-40 and the access opportunity 66-82 defined by the selected time slot 30-34. Selecting a currently unused code (48-64) if available based on Transmitting the identifier of the selected code (48-64) from the base station (20), Receiving the identifier at the selected user equipment 22-26; Communicating data between the selected user equipment (22-62) and the base station (20) using the selected code. The method of claim 1, wherein the identifier is transmitted with an acknowledgment signal. The method of claim 1, wherein the identifier is transmitted in an acknowledgment signal and a collision resolution signal. The method of claim 1, wherein the identifier indicates a communication uplink spreading factor to be transmitted from the user equipment (22-26) to the base station (20). 2. The method of claim 1, wherein the transmitted signature (36-40) is selected from 16 signature sets and the selected one time slot (30-34) is selected from an eight time slot set. 3. The method of claim 2, wherein if a code associated with an access opportunity (116-120) is not available, a negative acknowledgment signal is sent indicating that the code is not available. 2. The method of claim 1, wherein the selected code (48-64) is used to define a downlink physical channel for downlink communication. 8. The system of claim 7, wherein the downlink physical channel is time multiplexed into time slots and the identifier is selected one of time slots for downlink communication between the base station 20 and the selected user equipment 22-26. Displaying a data transmission method. 3. The method of claim 2, wherein the positive response signal identifier is indicated by one selected from a set of phases of the positive response signal. 3. The method of claim 2, wherein the acknowledgment signal identifier is an extra bit added. 3. The method of claim 2, wherein the acknowledgment signal identifier is represented by one selected from the Golay order set (122). A base station 20 of a radio spread spectrum code division multiplexed access communication system 18, the communication system comprising: a receiver 176 for receiving access opportunities 66-82 and packet data over a common packet channel; A packet channel is defined by a set of codes 48-64 and has a plurality of access opportunities 66-82, each access opportunity 66-82 being a time slot 30-34 and a signature 38-40. In the base station defined by, Receive the signature 36-40 and the access opportunity 116-120 defined by the one time slot from the user equipment 22-26 in one of the time slots 30-34. A code selection controller 134 associated with the receiver 138 to select a currently unused code based on code association with the received access opportunity 66-82 to select a code if available in response; By having a transmitter 136 associated with the controller 134 that transmits the identifier of the selected available code to the user equipment 22-26, the transmitter 136 has user equipment 22 encoded with the selected code. -26) a base station for transmitting communications. 13. The sequence generator (94) of claim 12, which generates a replicator of the signature of the received access opportunity, A first mixer 96 for selectively inverting the signature replicator in response to the code selection; And a second mixer (98) for selectively mixing in-phase or quadrature phase carriers and the selectively inverted signature in response to the code selection to generate the identifier. A wireless spread spectrum code division multiplexed access communication system 18 having a base station 20 and a plurality of user equipments 22-26, wherein the system uses a common packet channel for communication, the common packet channel being predetermined Defined as a code set 48-64 and having a plurality of access opportunities 66-82, each access opportunity 66-82 defined as a time slot 30-34 and a signature 36-40; System 18 includes the plurality of user equipments 22-26 and the base station 20, Each of the plurality of user equipments 22-26 includes means 136 for transmitting a signature 36-40 in the selected one of the common packet channel time slots 30-34. In a connected communication system, Each of the plurality of user equipments 22-26 may Means (142) for receiving an identifier indicating the selected code; Means for communicating with the base station using the selected code (140), The base station, In response to receiving the transmitted signature, use a currently unused code, if available, based on a code association between the selected signature 36-40 and the access opportunity 116-120 defined by the selected time slot 30-34. Means (134) for determining the selected code by selecting; Means (136) for transmitting an identifier of the selected code; Means (136) for communicating with the user equipment using the selected code. 15. The system of claim 14, wherein the identifier indicates a communication uplink spreading factor to be transmitted from the user equipment (22-26) to the base station (20). 15. The spread spectrum code of claim 14, wherein the transmitted signatures 36-40 are selected from 16 signature sets and the selected one time slot 30-34 is selected from 8 time slot sets. Division Multiplexed Access Communication System. 15. The apparatus of claim 14, wherein the base station 20 sends means 134, 136 for sending a negative acknowledgment signal indicating that codes are not available if codes associated with the access opportunity 116-120 are not available. The wireless spread spectrum code division multiplexed access communication system further comprising. 15. The system of claim 14, wherein the selected code (48-64) is used to define a downlink physical channel for downlink communication. 19. The apparatus of claim 18, wherein the downlink physical channel is time multiplexed into time slots, the identifier indicating a selected one of time slots for downlink communication between the base station 20 and user equipment 22-26. And a wireless spread spectrum code division multiple access access communication system. 15. The system of claim 14 wherein the acknowledgment signal identifier is represented by one selected from a set of phases of the acknowledgment signal. 15. The system of claim 14 wherein the acknowledgment signal identifier is an extra bit added to the acknowledgment signal. 15. The system of claim 14 wherein the acknowledgment signal identifier is represented by one selected from a high-order order set. delete delete delete delete delete